The emerging competitive metropolitan communications market has created a new set of challenges for carriers. Explosive demand for bandwidth together with regional fiber exhaustion is fueling the emergence of dense wavelength division multiplexing (DWDM) in metropolitan networks. Metropolitan DWDM networks require high levels of wavelength termination diversity, optical simplicity, low entry costs and unobtrusive network upgrades.
Traditional WDM approaches tailored to xe2x80x9clong haulxe2x80x9d networks address the network as a composite set of individually engineered wavelengths. Many WDM devices are passive devices. A lightpath is an optical carrier modulated with data for transport which is frequency multiplexed into the optical media with other lightpaths by the WDM device. There are typically two types of optical processing devices employed in such networksxe2x80x94large, fixed size add/drop multiplexers and cascaded, individual wavelength add/drop devices.
The large, fixed size add/drop multiplexer (FIG. 1) has relatively high cost but relatively low insertion loss. Because a large number of wavelengths are provisioned initially (greatly exceeding the initial need), future growth can be achieved without interruption by lighting up initially unused wavelengths. This type of device typically terminates or originates all of the wavelengths in a network fiber. Some wavelengths may still be implemented in a through path as shown for wavelengths xcex1, xcex2, xcex3 while other wavelengths are added or dropped as shown for wavelength xcex8. Larger devices having 16 to 32 ports are now typically available.
Individual wavelength add/drop devices can be cascaded as growth is required. Such an arrangement of devices is shown in FIG. 2. These devices typically have a through-path containing wavelengths not redirected by the cascaded devices. When cascaded at a node, the aggregate of cascaded devices quickly develops high insertion loss that is undesirable and costly to accommodate. The existing services often must be interrupted in order to provision new ones. A smaller number of wavelengths are selected in this type of network node than are typical in a node that uses the large, fixed size device of FIG. 1, therefore only half as many wavelengths are indicated.
Some networks use both approaches. The add/drop device of FIG. 1 is used at many points in such networks because of the need for growth allowance without future network disruptions. At the same time, limited deployment of the add/drop devices of FIG. 2 allows for low cost nodes that are unscalable.
In other optical networks, optical banding is used to drop a single band of wavelengths at a node and passively forward other bands through to the next node in the network. This approach provides for lower insertion loss in the optical through path. However, optical signal regeneration can still be required for connecting pairs of nodes separated by intervening nodes in certain network topologies.
WDM allows concurrent use of the same physical fiber by different signals on different wavelengths. A first division occurs between the two major windows of optical fiber: 1300 nm window, with laser operation commonly in the range of 1280 to 1350 nm; and 1550 nm window, with laser operation commonly in the range of 1530 to 1560 nm. These two windows provide a first level of multiplexing. Operation at multiple wavelengths is not common in the 1300 nm window as devices are often poorly controlled. However, within the 1550 nm window it is common to have 40 to 80 wavelengths (lightpaths).
The complexity of an optical network topology increases dramatically with the deployment of WDM and DWDM technology. Optical networks contain several to many nodes which can be interconnected into a ring (e.g., SONET ring) or a mesh topology. When WDM or DWDM is deployed, the actual logical interconnection of these nodes can be different than the physical cable topology. Complex optical configurations result and configuration information for the optical paths becomes very difficult to derive.
There is a need to reduce optical losses in the through path of optical network configurations such that the use of optical regeneration is reduced or avoided.
There is also a need to provide information to a network management application to detect misconfigured networks and predict which lightpaths are co-resident in a single fiber.
Accordingly, a communication system includes plural nodes interconnected with an optical transmission medium capable of carrying plural bands of optical channels. A device at each node is coupled to the medium for dropping one or more bands, adding one or more bands, and passively transmitting other bands such that a pair of nodes can communicate directly using a band common to the respective bands. A node can communicate with multiple nodes using a single band element in its through path and at its location.
According to one aspect of the system, one band of the bands associated with each of a first set of nodes overlaps with one band of the bands associated with each of a second set of nodes. In a network configuration, adjacent nodes can communicate using an overlapping band. In another network configuration in which the nodes of the first set of nodes are non-adjacent to each other and the nodes of the second set of nodes are non-adjacent to each other, a node from the first set can communicate with a node from the second set using the overlapping band. The system can include multiple overlapping bands to provide a high level of wavelength termination diversity.
According to another aspect of the system, each node can include a first channel filter for separating at least one individual optical channel within the bands dropped by the device. Each node can further include a second channel filter or power coupler for adding at least one individual optical channel to the bands added by the device.
A method of the present approach includes providing plural nodes interconnected by an optical transmission medium capable of carrying plural bands of optical channels; at each node, dropping one or more bands, adding one or more bands, and passively transmitting other bands; and communicating between a pair of nodes using a band common to the respective bands.
It should be recognized that tradeoffs associated with an optical infrastructure can be dependent upon the physical network topologies. Optimizations can vary with different customer requirements and topologies. The overlapped optical banding of the present system and method provides improved optical performance by minimizing implementation costs with scalability, especially for entry-level configurations, and by minimizing optical losses in the through path to provide greater optical span length. A further benefit of the present approach is that incremental optical network bandwidth can be achieved without interruption of existing services. Applications of the present system and method with overlapped optical banding include ring and mesh topologies.
According to an optical management bus system and method, connection of plural hybrid optical/electrical cables between transmission equipment and optical devices which connect to network fibers provides a set of electrical connections that can be used to ascertain optical interconnections in an optical shelf configuration.
According to an aspect of the optical management bus approach, an optical module includes two electrical paths which are interconnected and a third electrical path isolated from the first two electrical paths. The electrical paths form electrical busses without stubs.
Memory devices each containing an identifier are connected to the electrically isolated busses within one optical module so that the information collected on the independent bus segments may be associated to provide a concise map of the optical interconnections and the order of interconnected optical modules to be ascertained. According to the present system and method, a particular optical module can be identified as the root of an optical branching tree at a node and thereby the unique termination point of a network fiber such that a physical fiber topology can be associated with the logical fiber topology.